In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultra violet radiation typified by g-line and i-line radiation has been used, but nowadays, mass production of semiconductor elements using KrF excimer lasers and ArF excimer lasers has commenced. Furthermore, investigation is also being conducted into radiation with even shorter wavelengths than these excimer lasers, including F2 excimer lasers, electron beams, EUV (extreme ultra violet), and X-rays.
Furthermore, one example of a known pattern-forming material capable of forming a pattern of minute dimensions is a chemically amplified resist, which includes a base material component with a film-forming capability, and an acid generator component that generates acid upon exposure. Chemically amplified resists include negative resists, which undergo a reduction in alkali solubility upon exposure, and positive resists, which display increased alkali solubility upon exposure.
Conventionally, polymers have been used as the base material components within these types of chemically amplified resists, and examples of these polymers include polyhydroxystyrene (PHS), PHS-based resins in which a portion of the hydroxyl groups of a PHS have been protected with acid-dissociable, dissolution-inhibiting groups, copolymers derived from (meth)acrylate esters, and resins in which a portion of the carboxyl groups within these (meth)acrylate esters have been protected with acid-dissociable, dissolution-inhibiting groups.
However, when a pattern is formed using these types of pattern-forming materials, a problem arises in that roughness can develop on the upper surface and side wall surfaces of the pattern. For example, roughness on the side wall surfaces of a resist pattern, so-called line edge roughness (LER), can cause distortions around the holes in hole patterns, and fluctuations in the line width in line and space patterns, and consequently has the potential to adversely affect the formation of very fine semiconductor elements.
This problem becomes more significant as the pattern dimensions are reduced. Accordingly, in lithography processes using electron beams or EUV or the like, which are targeting the formation of very fine patterns with dimensions of several tens of nm, very low levels of roughness that are superior to current levels of pattern roughness are being demanded.
However, the polymers typically used as base materials have a large molecular size (or root mean squared radius per molecule) of several nm. In the developing step of a pattern formation process, the solubility behavior of the resist with respect to the developing solution typically occurs in single molecule units of the base material component, meaning that as long as polymers are used as the base material component, further reductions in the level of roughness will remain extremely difficult to achieve.
In order to overcome this type of problem, resists that employ a low molecular weight material as the base material component have been proposed as potential materials for achieving lower levels of roughness. For example, non-patent references 1 and 2 propose low molecular weight materials that include alkali-soluble groups such as hydroxyl groups or carboxyl groups, wherein either a portion of, or all of, these groups have been protected with acid-dissociable, dissolution-inhibiting groups.
[Non-Patent Reference 1] T. Hirayama, D. Shiono, H. Hada and J. Onodera: J. Photopolym. Sci. Technol., 17 (2004), p. 435
[Non-Patent Reference 2] Jim-Baek Kim, Hyo-Jin Yun, Young-Gil Kwon: Chemistry Letters (2002), pp. 1064 to 1065.